Non-virulent Porphyromonas gingivalis mutant

ABSTRACT

The  Porphyromonas gingivalis  strain which is deposited at ATCC under accession number 202109. A pharmaceutical composition comprising the  Porphyromonas gingivalis  strain of the present invention.

CROSS-REFERENCE TO RELATED APPLICATION

The present Application is a divisional application of U.S. patent application Ser. No. 09/133,089, filed Aug. 12, 1998, entitled “Nonvirulent Strain of P. Gingivalis,” now U.S. Pat. No. 6,254,863, issued Jul. 3, 2001 the contents of which is incorporated herein by reference in their entirety.

BACKGROUND

Periodontitis is an inflammatory disease of the tissues surrounding the teeth characterized by loss of the periodontal ligament attachment and alveolar bone support of the tooth. Periodontitis affects more than 49 million people in the United States and hundreds of millions of people worldwide and has been reported as a risk factor for cardiovascular disease and pre-term delivery of low-birth-weight infants. The most common cause of periodontitis is chronic Gram-negative bacterial infections. Among the Gram-negative bacteria implicated as a cause of periodontitis, Porphyromonas gingivalis is the major component of the flora in over 90% of adult periodontitis lesions.

Besides being a major etiological agent in adult human periodontitis, Porphyromonas gingivalis also causes aspiration pneumonia and necrotizing pneumonia, abscesses in brain, genitourinary tract and lung, as well as mediastinitis. By contrast, P. gingivalis is not normally found at healthy sites nor is it found in patients with gingivitis but with no accompanying periodontitis.

The current therapy for periodontitis is directed toward identifying, removing and controlling the etiologic factors, and then correcting the defects these pathogens have caused. These therapies include scaling and root planing, chemotherapy, periodontal surgery and periodic maintenance therapy. However, these treatments are not entirely effective because, for example, the pathogens can become resistant to chemotherapeutic agents.

Several potential virulence factors have been identified which appear to relate to the pathogenicity of P. gingivalis in periodontitis. These factors include fimbriae (adhesins), capsule (antiphagocytosis), lipopolysaccharide (bone resorption), proteases (specific and generalized tissue destruction) and a variety of toxic by-products (e.g., ammonia). Some of these factors have been purified and biochemically characterized. However, the specific roles, interactions, relative importance and regulation of these factors remains to be determined.

Therefore, there remains a need for effective prevention and treatment for periodontitis. Further, there remains a need for a modified strain of P. gingivalis that can be used as a host genetic background to determine the specific roles, interactions, relative importance and regulation of the potential virulence factors produced by wild-type P. gingivalis.

SUMMARY

According to one embodiment of the present invention, there is provided a nonvirulent, recA defective mutant of Porphyromonas gingivalis. According to another embodiment of the present invention, there is provided a Porphyromonas gingivalis strain which is deposited at ATCC under accession number 202109.

According to another embodiment of the present invention, there is provided a pharmaceutical preparation comprising a mutant of Porphyromonas gingivalis according to the present invention.

According to another embodiment of the present invention, there is provided a method of decreasing the growth rate or reproduction rate of Porphyromonas gingivalis in a mammal, such as a human. The method comprises the step of administering to the mammal at least one dose of a non-virulent, recA defective mutant of Porphyromonas gingivalis, such as at least one dose of a Porphyromonas gingivalis strain which is deposited at ATCC under accession number 202109.

According to another embodiment of the present invention, there is provided a method of preventing or treating a Porphyromonas gingivalis infection such as periodontitis in a mammal, such as a human. The method comprises the step of administering to the mammal at least one dose of Porphyromonas gingivalis according to the present invention.

The methods of the present invention can be performed by administering to the mutant with the at least one dose of a non-virulent, recA defective mutant of Porphyromonas gingivalis via a route selected from the group consisting of a subcutaneous route, an intravenous route and an intramuscular route, among other routes. In a preferred embodiment, the methods of the present invention include administering at least one dose of a non-virulent, recA defective mutant of Porphyromonas gingivalis, wherein the dose is between about a 1×10³ and 1×10⁷ bacteria per kg of body weight of the mammal. More preferably, the dose is between about 1×10⁵ and 1×10⁶ bacteria per kg of body weight of the mammal.

FIGURES

These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying figures where:

FIGS. 1 and 2 show the results of Southern blot analyses of allelic exchange mutants of P. gingivalis to confirm the presence of the ermF-ermAM cassette in a predicted location;

FIG. 3 is a bar graph showing the results of an assay for arginine specific proteolytic activity of P. gingivalis FLL32, FLL33 and W83 in the presence or absence of L-cysteine;

FIGS. 4 and 5 are bar graphs showing the results of an assay for the localization of arginine-specific proteolytic activity and for lysine-specific proteolytic activity, respectively, of P. gingivalis FLL32, FLL33 and W83 in the presence or absence of L-cysteine;

FIGS. 6 and 7 show the results of Northern blot analyses of prpRI and prtP protease genes, respectively, of P. gingivalis FLL32, FLL33 and W83;

FIG. 8 shows the results of an analysis by SDS-PAGE of the ability of P. gingivalis FLL32, FLL33 and W83 to degrade purified C3 complement protein; and

FIG. 9 is a graph showing the results of accumulation of C3 fragments on the bacterial surface of FLL32, FLL33 and W83.

DESCRIPTION

The present invention involves the discovery of a non-virulent mutant of Porphyromonas gingivalis. This mutant, designated FLL32, has been found to convey protection against the wild-type Porphyromonas gingivalis W83 in mammals when the mammal was immunized with the mutant strain FLL32. Further, FLL32 can be used as a host genetic background to determine the specific roles, interactions, relative importance and regulation of the potential virulence factors produced by wild-type P. gingivalis.

All publications mentioned in this document are incorporated by reference in their entirety.

A deposit of Porphyromonas gingivalis mutant strain FLL32 has been made at the ATCC depository, 10801 University Blvd., Manassas, Va., US 20110-2209 on Apr. 8, 1998, under the accession number 202109. This deposit shall be viably maintained, replacing it if it becomes non-viable, for a period of 30 years from the date of the deposit, or for 5 years from the last date of request for a sample of the deposit, whichever is longer, and made available to the public without restriction in accordance with the provisions of the law. The Commissioner of Patents and Trademarks, upon request, shall have access to the deposit.

In summary, the FLL32 strain was isolated during construction of a mutant recA⁻ mutant of P. gingivalis W83 wild-type by allelic exchange mutagenesis. The FLL32 strain was recA⁻ and lacked black pigmentation and β-hemolytic activity on blood agar. Further, the FLL32 strain was deficient in proteolytic activity and significantly more sensitive to UV irradiation than the wild-type W83 strain.

The FLL32 strain exhibited substantially reduced virulence when introduced into mammals and protected those animals immunized with that strain against subsequent infection by the wild-type strain W83. Further, in Western blot experiments of whole cell extracts, unique immunoreactive bands were found in FLL32 using sera from immunized animals. The FLL32 strain is the first nonvirulent recap strain of P. gingivalis shown to protect mammals against subsequent infection by the wild-type P. gingivalis.

Isolation and Characterization of P. gingivalis FLL32 Strain

Porphyromonas gingivalis FLL32 was isolated and characterized as follows. First, the recA homolog gene was cloned from wild-type W83. Next, the recA homolog gene was sequenced. Then, an isogenic recA⁻ mutant of P. gingivalis W83 designated FLL32 was constructed by allelic exchange mutagenesis and the presence of the defective recA DNA in the P. gingivalis FLL32 strain confirmed by Southern blot analyses.

Next, the phenotype and UV sensitivity of P. gingivalis FLL32 strain was determined, as well as its arginine and lysine specific proteolytic activity. Additionally, the amount of its mRNA transcript for the major protease genes was determined. Then, the amount of its C3 complement protein degradation was determined and the amount of C3 accumulation on the surface of the P. gingivalis FLL32 strain was determined. Finally, the virulence of the P. gingivalis FLL32 strain and protective effect of immunization by the FLL32 strain against subsequent challenge by the wild-type was examined.

(a) Cloning of the recA Homolog Gene from P. gingivalis W83

The recA homolog gene was cloned from P. gingivalis W83 as follows. First, degenerate oligonucleotide primers (Dybvig, K., et al., “Degenerate oligonucleotide primers for enzymatic amplification of recA sequences from gram-positive bacteria and mycoplasmas.” J.Bacteriol. 174, 2729-2732, 1992) were used in a polymerase chain reaction (PCR) to amplify a 320 bp fragment of the recA sequence of P. gingivalis W83. This PCR fragment was ³²P-labeled and used to screen a λ DASH recombinant phage bank P. gingivalis W83 for the presence of hybridizing clones. Ten of 1×10³phage clone plaques (1.0%) hybridized with the probe.

The hybridizing phage plaques were then amplified and absorbed onto maltose-grown E. coli cells. DNA from the phage clones was isolated using the Promega Lambda Wizard DNA Purification system (Promega, Corporation, Madison, Wis.). NotI-BamHI cleavage of purified DNA from two of the recombinants, designated L2 and L10, revealed that the phage clones had different restriction fragment patterns. L2 contained an 8.0 kb and a 6.5 kb fragment that were missing in L10, while L10 contained an 11 kb, a 5.8 kb and a 0.3 kb fragment that were missing in L2. Both L2 and L10 contained a similar 2.1 kb fragment. These data indicated that the L2 and L10 clones were independent clones and not siblings from a single cloning event.

The L10 clone was chosen for further study because it had the smaller fragment insert. Southern blot hybridization using the ³²P-labeled 0.3 kb PCR fragment of the recA gene from the chromosome of W83 was used as a probe to identify the hybridizing fragment. The plasmid pUC19 was used to subclone a 2.1 kb hybridizing BamHI fragment from L10. This clone was designated pFLL26.

(b) Nucleotide Sequencing of the recA Homolog Gene

Both strands of the 2.1 kb hybridizing BamHI fragment from the L10 clone carried on pFLL26 were sequenced and one 1.02 kb open reading frame corresponding to a 36 kDa protein was detected, GenBank Accession Number U70054 (Fletcher et al., 1997). There was a start codon at base position 774. A purine-rich sequence found in E. coli ribosome binding sites was also seen three bases upstream from the initiation site. Sequences resembling procaryotic −10 and −35 promoter regions were detected at base positions 749 and 729 respectively. The calculated G+C ratio for the recA homolog gene was 50% which is close to the ratio of 46 to 48% previously reported for genomic P. gingivalis DNA (Shah and Collins, 1988).

A comparison of the amino acid sequence of this gene with the National Center for Biotechnology Information genetic sequence databank revealed a similarity of approximately 90, 86 and 82 percent to the RecA proteins from Bacteroides fragilis, Prevotella ruminicola, GenBank Accession Number U21227, and Mycobacterium smegmatis, GenBank Accession Number X99208, respectively. (Goodman and Woods, Molecular Analysis of the Bacteroides fragilis recA Gene, Gene 94, pp. 77-82, 1990) Further, regions between amino acids 68 to 81 and 266 to 288 revealed conserved ATP binding domains.

(c) Construction of a recA⁻Mutant in P. gingivalis W83

An isogenic recA⁻ mutant of P. gingivalis W83 was constructed by allelic exchange mutagenesis as follows. The nucleotide sequence of the cloned recA fragment revealed a unique HincII restriction site at bp 435 of the open reading frame (Fletcher, H. M. et al., “Nucleotide sequence of Porphyromonas gingivalis W83 recA homolog and construction of a recA-deficient mutant.” Infect.Immun. 65, 4592-4597, 1997). To utilize this site, a 1.8 kb EcoRI-PstI fragment containing the intact recA gene was subcloned into EcoRI-PstI cleaved pUC19. The resulting plasmid, pFLL23, was digested with HincII and ligated with the 2.1 kb ermF-ermAM cassette from pVA2298 to produce recombinant plasmid designated pFLL24. (See Fletcher, H. M., Schenkein, H. A., Morgan, R. M., Bailey, K. A., Berry, C. R., and Macrina, F. L. (1995). Virulence of a mutant of Porphyromonas gingivalis W83 that is defective in the prtH gene. Infect.Immun. 63, 1521-1528).

Then, the recombinant plasmid pFLL24 was used as donor DNA in electroporation of P. gingivalis W83. Since the pFLL24 plasmid was unable to replicate in P. gingivalis, Clindamycin resistant (Cc^(r)) transformants could only arise as a result of an integration into the wild-type gene on the chromosome. Two double crossover events were predicted between the regions flanking the erm marker and the wild-type recA gene on the chromosome that would result in a replacement of a segment of the wild-type gene with a fragment conferring clindamycin resistance.

Following electroporation and plating on selective medium, 15 Cc^(r) colonies were detected after a 7 day incubation period. These colonies were replica plated onto selective medium and exposed to UV light to determine their sensitivity. Four UV sensitive colonies, designated FLL32, FLL33, FLL34 and FLL35, were chosen from the unexposed plate for further study.

To confirm the presence of the ermF-ermAM cassette in the predicted location, that is interrupting the recA DNA, Southern blot analyses were performed on the total cellular DNA from P. gingivalis wild-type W83, as a control, and from the Cc^(r) transformants FLL32, FLL33, FLL34 and FLL35. Their DNA was cleaved with BamHI, electrophoresed through 0.7% agarose, bidirectionally transferred to nitrocellulose and probed with ³²P labeled pFLL23 and pVA2198. If the DNA was digested with BamHI, a predicted 2.1 kb fragment would be seen. If the DNA was not digested with BamHI, a predicted 4.2 kb fragment would be seen. Since the ermF-ermAM cassette is missing a BamHI site, any of the four Cc^(r) transformants with the ermF-ermAM cassette interrupting the recA DNA sequence should have shown a 4.2 kb fragment but not a 2.1 kb fragment.

Referring now to FIGS. 1 and 2, there are shown the results of the Southern blot analyses of allelic exchange mutants of P. gingivalis to confirm the presence of the ermF-ermAM cassette in the predicted location. As can be seen in FIG. 1, the predicted 2.1 kb fragment was seen in the wild-type P. gingivalis W83, lane A, using the ³²P-labeled pFLL23 that carries the P. gingivalis recA homolog as a probe, indicated the presence of the recA DNA. In contrast, a 4.2 kb fragment was present in each of the four Cc^(r) mutants of W83, lanes B-E, FLL32, FLL33, FLL34 and FLL35, respectively, and indicated the presence of the recA DNA sequence interrupted by the ermF-ermAM cassette.

As can be seen in FIG. 2, using pVA2198, which carried the ermF-ermAM cassette as a probe, revealed an identical 4.2 kb hybridizing fragment present in the four Cc^(r) mutants, lanes B-E, FLL32, FLL33, FLL34 and FLL35, respectively, but not in the wild-type W83, lane A, indicating the presence of the ermF-ermAM cassette only in the transformants. pUC19 vector sequences used as a control did not hybridize with W83 or any of the four Cc^(r) mutants, FLL32, FLL33, FLL34 and FLL35 (data not shown). These data indicated that recombination had occurred in the four Cc^(r) mutants, FLL32, FLL33, FLL34 and FLL35, resulting in the wild-type recA gene being interrupted by the ermF-ermAM cassette in FLL32, FLL33, FLL34 and FLL35.

(d) Phenotypic Characterization of P. gingivalis W83 recA Mutants

The phenotype of P. gingivalis W83 recA mutants were initially characterized as follows. The recA mutants, FLL32, FLL33, FLL34 and FLL35, were plated on Brucella blood agar plates (Anaerobic Systems, Inc., San Jose, Calif.) to determine if any pleotropic effects were associated with inactivation of the recA gene. Two classes of mutants were observed. The first class, a single colony FLL32, was unpigmented and displayed significantly less β-hemolysis than the wild-type W83. The second class contained three strains, FLL33, FLL34 and FLL35, all of which displayed similar β-hemolytic activity and black pigmentation as the wild-type W83. FLL32 and FLL33 were chosen for further study as representatives of their respective classes. A generation time of 3 hours was determined for W83 and of 3.5-4 hours for both FLL32 and FLL33.

(e) Determination of the UV Sensitivity of P. gingivalis W83 recA Mutants

To confirm the loss of activity of the P. gingivalis RecA protein, the relative sensitivity of the wild-type and recA⁻ strains to UV irradiation was determined as follows. Wild-type W83 and recA⁻ mutants FLL32 and FLL33 were exposed to 1000 μjoules of UV irradiation. There was an 80% survival of the wild-type W83 strain in contrast to the 18% survival for FLL32 and FLL33. When wild-type W83 and mutants FLL32 and FLL33 were exposed to 2000 μjoules of UV irradiation, there was 40% survival of the wild-type W83 cells compared to 0% survival for the recA⁻ mutants FLL32 and FLL33. These data indicated that the recA gene of P. gingivalis W83 plays an important role in repairing DNA damage caused by UV irradiation and that both FLL32 and FLL33 were recA defective.

(f) Determination of the Arginine and Lysine Specific Proteolytic Activity of FLL32, FLL33 and W83

The arginine specific proteolytic activity of P. gingivalis W83 recA mutants was determined by assaying whole cell preparations from each of the three strains of P. gingivalis, FLL32, FLL33 and W83 for proteolytic activity using N-α-benzoyl-DL-arginine p-nitroanilide (BAPNA). Each strain of P. gingivalis was grown for 48 hours to late log phase (OD₆₀₀ of 1.2) in 500 ml BHI broth supplemented with hemin and vitamin K. The cells were then washed in PBS (pH 7.3) and resuspended to an OD₆₀₀ of 0.3. 50 μl of the cell samples were incubated for 10 min at 37° C. in 50 mM Tris-HCl (pH 7.0), and 1 mM α-N-benzoyl-arginine-DL-p-nitroanilide (BAPNA) in the presence or absence of 0.5 mM L-cysteine. The control contained buffer alone. Hydrolysis of BAPNA was monitored by the change of absorbance at 410 nm.

Referring now to FIG. 3, there is shown a bar graph of the assay results. As can be seen, the wild-type W83 (−Cys) showed more proteolytic activity than FLL33 (−Cys), while FLL32 (−Cys) did not show significantly more proteolytic activity than the control. The activity from all three strains was enhanced in the presence of cysteine (+Cys) but the relative rates of proteolytic activity remained the same. The reduction of proteolytic activity seen in FLL33 compared to W83 could be related to the longer generation time for the recA⁻ strains compared to the wild-type W83.

Localization of the arginine-specific proteolytic activity and for lysine-specific proteolytic activity in the recA⁻ strains was determined as follows. First, extracellular proteolytic activity was tested. Ammonium sulfate was added to 500 ml of culture supernatant from cells grown to late log phase (OD₆₀₀ of 1.2) to 100% saturation. The precipitate was resuspended in 3 ml of PBS (pH 7.3), dialyzed against the same buffer, and then stored at −20° C.

Referring now to FIGS. 4 and 5, there are shown bar graphs showing the results of an assay for the localization of arginine-specific proteolytic activity and for lysine-specific proteolytic activity. As can be seen, the FLL33 showed more extracellular arginine-specific proteolytic activity and more lysine-specific proteolytic activity than the wild-type W83 (−Cys). FLL32 did not show significantly more arginine-specific proteolytic activity or lysine-specific proteolytic activity than the control. Further, the extracellular arginine-specific proteolytic activity of both W83 and FLL33, but not FLL32, was enhanced in the presence of cysteine (+Cys).

Next, intracellular proteolytic activity was tested. The cells from the above experiment were washed in PBS (pH 7.4), and then resuspended in the same buffer to a final volume of 10 ml. 1 ml aliquots were transferred to microcentrifuge tubes containing 0.5 volume of 0.1 mm zirconium beads (Biospec Products, Inc. Bartlesville, Okla.), then lysed in a Mini-Bead Beater homogenizer (Biospec Products) for 3 min. Beads and cellular debris were removed by centrifugation at 12,000×g for 5 min to obtain a clear lysate. Using 100 μg of protein per assay, similar intracellular arginine- and lysine-specific proteolytic activities were observed for the W83 and FLL33 strains, but there was no significant intracellular arginine- or lysine-specific proteolytic activities for FLL32 (data not shown).

(g) Comparison of the Presence and Amount of mRNA Transcript for the Major Protease Genes in FLL32, FLL33 and W83

The loss of proteolytic activity in strain FLL32 could have resulted either from a lack of transcription or translation of the gene, or from a lack of post-translational activation of the precursor product. In order to determine the cause of the loss of proteolytic activity in FLL32, the presence and amount of mRNA transcript for the major protease genes in FLL32, FLL33 and W83 was determined as follows.

First, total RNA was isolated using the Qiagen RNeasy Kit (Qiagen, Valencia, Calif.) from the wild-type W83 strain and from the FLL32 and FLL33 mutants grown to mid-log phase (OD₆₀₀ of 0.2). Unique oligonucleotide primers for prtP (as disclosed in Barkocy-Gallagher, G. A. et al., “Analysis of the prtP gene encoding porphypain, a cysteine proteinase of Porphyromonas gingivalis.” J. Bacteriol. 178, 2734-2741, 1996), prpRI (Aduse Opoku, J. et al., “Characterization, genetic analysis, and expression of a protease antigen (PrpRI) of Porphyromonas gingivalis W50.” Infect.Immun. 63, 4744-4754, 1995) and prtRII were used in RT-PCR to amplify a 1 kb region of the transcripts. Amplified products of the predicted 1 kb size were observed for all three protease gene transcript in all three strains (data not shown). Further, there were no observed differences seen in the concentration of the amplified product between the genes of the three strains. Therefore, both FLL32 and FLL33 strains produce the same mRNA transcripts for the major protease genes in the same amounts as the wild-type W83. As a control, recA intragenic primers amplified the expected 0.72 kb region only in the wild-type W83 strain.

The presence of the mRNA transcripts for the prpRI and prtP proteases in all three P. gingivalis strains were further confirmed in Northern blot analysis using an amplified intragenic region of each gene as a probe. Total RNA was extracted from each of the W83, FLL32 and FLL33 strains grown to mid-log phase (OD₆₀₀ of 0.2) using the Qiagen RNeasy midi kit (available from Qiagen, Valencia, Calif., according to the manufacturer's instructions). RNA samples of 1 μg were then separated by agarose gel electrophoresis and transferred to nitrocellulose filter according to the method of Sambrook et al. (Sambrook, J., Fritsch, E. F., and Maniatis, T. (1989). Molecular Cloning: A Laboratory Manual. Second edition. (Cold Spring Harbor, N.Y.: Cold Spring Harbor Laboratory Press)).

Referring now to FIGS. 6 and 7, there are shown the results of the Northern blot analysis of prpRI and prtP protease genes from the three strains of P. gingivalis W83, FLL33 and FLL32. FIG. 6 shows the results using a ³²P-labeled specific intragenic region of prpRI as the probe. FIG. 7 shows the results using a ³²P-labeled specific intragenic region of prpP as the probe. The size of the transcripts in kb are given in the left margins. Lane A shows the results for the W83 wild-type strain, lane B shows the results for the FLL32 mutant strain and lane C shows the results for the FLL33 mutant strain.

As can be seen in FIG. 6, the prpRI probe hybridized to 6.3 and 4.2 kb transcripts. As can be seen in FIG. 7, the prtP probe hybridized to 6.6, 4.3 and 3.2 kb transcripts. The 6.3 and 6.6 kb transcripts for the prpRI and prtP genes, FIGS. 6 and 7 respectively, are consistent with the known size of those genes transcripts. The presence of the smaller transcripts could be degraded product or could be transcripts that share regions of homology with the protease genes. These results confirm the presence of the mRNA transcripts of the prpRI and prtP protease genes in all three strains of P. gingivalis, W83, FLL32 and FLL33.

(h) Determination of the C3 Complement Protein Degradation of FLL32, FLL33 and W83

The ability of P. gingivalis FLL32, FLL33 and W83 to degrade purified C3 complement protein was determined as follows. 1 mg/ml of C3 was incubated with increasing dilutions of each strain at 37° C. for 30 minutes and the supernatant were analysed by SDS-PAGE with 10% separation gels and strained with comassie. The results are shown in FIG. 8 using C3 alone as a control (lane 1), 10⁹ W83 cells/ml (lane 2), 5×10⁸ W83 cells/ml (lane 3), 10⁸ W83 cells/ml (lane 4), 10⁹ FLL32 cells/ml (lane 5), 5×10⁸ FLL32 cells/ml (lane 6), 10⁸ FLL32 cells/ml (lane 7), 10⁹ FLL33 cells/ml (lane 8), 5×10⁸ FLL33 cells/ml (lane 9) and 10⁸ FLL33 cells/ml (lane 10).

As can be seen, the highest concentration of W83 tested (lane 2) completely degraded the α-chain of C3 with generation of C3b and some lower molecular mass fragments similar to C3c and C3d. The lowest bacterial concentration of W83 tested (lane 4) partially degraded the α-chain, causing both α and α′-chains to be visible. Similar results were observed for FLL33 (lanes 8-10). In contrast, the highest concentration of FLL32 (lane 6) only minimally degraded C3 to C3b and lower molecular mass cleavage fragments. There was no degradation of C3 at the lowest bacterial concentration tested for FLL32. Thus, FLL32 is less capable of degrading C3 than either the wild-type W83 or FLL33.

(i) Assessment of C3 Accumulation on FLL32, FLL33 and W83

Opsonization of P. gingivalis strains W83, FLL32 and FLL33 was assessed for the accumulation of C3 fragments on the bacterial surface as follows. 5×10⁸ cells/ml of each strain was incubated in pooled human serum that was diluted 1:3 with Veronal-buffered saline (0.01 M Veronal buffer, pH 7.5, containing 0.13 M NaCl) and that contained 2 μg/ml ¹²⁵I-C3 for 35 minutes. The incubated bacterial samples were then washed and assessed for bound ¹²⁵I-C3 fragments by scintillation counting. Referring now to FIG. 9, it can be seen that W83 failed to accumulate substantial amounts of C3 by the end of the incubation period. In contrast, FLL33 accumulated 3×10⁴molecules/bacterium and FLL32 accumulated 6×10⁴ molecules/bacterium of ¹²⁵I-C3 fragments. Taken together, these results suggest that FLL32 has an increased capacity to be opsonized with C3 fragments compared to both W83 and FLL33.

EXAMPLE I Comparison of the Virulence Between FLL32, FLL33 and W83 in a Mammal

A first comparison of the virulence between wild-type W83, mutant strain FLL32 and mutant strain FLL33 Porphyromonas gingivalis in a mammal was made as follows. Sixteen female Balb/c mice (8-10 weeks old, Harlan Sprague Dawley Inc., Indianapolis Ind.) were divided into three groups, five in Group I, five in Group II and six in Group III. Each animal received a single challenge dose of 1×10¹⁰ bacteria P. gingivalis W83 (Group I), FLL33 (Group II) or FLL32 (Group III) by subcutaneous, dorsal surface injection, a dosage of approximately 2×10⁴ bacterial per kg body weight.

At 24 hours post-challenge, two of the five animals in Group I and one of the five animals in the Group II had died and the remaining animals in both Groups I and II appeared cachectic and hunched with ruffled hair. Although the animals did not display lesions at the dorsal surface site of injection (primary site), all had developed spreading, ulcerative abdominal skin lesions (secondary site). All of the remaining animals in the Group I and three of the four remaining animals in the Group II died by 48 hours post-challenge. The fifth animal in the Group II died by the fourth day post-challenge.

In contrast, all six of the animals in Group III challenged with FLL32 survived the 14 day post-challenge observation period. None of the animals in Group III had any observable negative effects from the challenge.

The data from these challenges were analyzed using Fisher's Exact Test. The analysis found no difference in the virulence between W83 and FLL33 (p=1.000). However, the FLL32 strain had a statistical difference in virulence when compared to FLL33 (p=0.002) and W83 (p=0.002).

A second comparison of the virulence between wild-type W83, mutant strain FLL33 and mutant strain FLL32 Porphyromonas gingivalis in a mammal was made as follows. Seventeen mice Balb/c mice (8-10 weeks old, Harlan Sprague Dawley Inc., Indianapolis Ind.) were divided into three groups, five in Group IV, six in Group V and six in Group VI. Each animal received a single challenge dose of 5×10⁹ bacteria P. gingivalis W83 (Group IV), FLL33 (Group V) or FLL32 (Group VI) by dorsal subcutaneous surface injection.

At 24 hours post-challenge, one of five animals in Group IV had died and the remaining four had developed ulcerated abdominal skin lesions. By 48 hours post-challenge, three of the remaining animals in Group IV had died. The lesions in the surviving fifth animal were resolving at day 14 post-challenge.

At 24 hours post-challenge, one of six animals in Group V had died and the remaining five had developed ulcerated abdominal lesions. By 48 hours post-challenge, three of the five remaining animals in Group V had died. One additional animal died by day 5 post-challenge. The lesions in the surviving sixth animal were resolving at day 14 post-challenge.

In contrast, all six of the animals in Group VI challenged with FLL32 survived the 14 day post-challenge observation period. None of the animals in Group VI had any observable negative effects from the challenge.

The results of these challenges were analyzed using Fisher's Exact Test. The analysis found no difference in the virulence between W83 and FLL33 (p=0.727). However, the FLL32 strain had a statistical difference in virulence when compared to FLL33 (p=0.008) and W83 (p=0.015).

As can be appreciated from this Example, the inactivation of the recA gene in P. gingivalis FLL33 did not significantly affect the virulence of P. gingivalis. However, the mutation in the FLL32 strain significantly affected the virulence of P. gingivalis.

EXAMPLE II Demonstration of the Protective Effect of Immunization with FLL32 Against Subsequent Challenge with Wild-Type W83 P. gingivalis

The protective effect of immunization of a mammal with FLL32 against subsequent challenge with wild-type W83 P. gingivalis was demonstrated as follows. Sixteen female Balb/c mice (8-10 weeks old, Harlan Sprague Dawley Inc., Indianapolis Ind.) were subcutaneously immunized once per week for 3 weeks with 1×10¹⁰ bacteria of the mutant strain FLL32, a dosage of 5×10⁵ bacteria per kg of body weight. Ten additional female Balb/c mice (8-10 weeks old, Harlan Sprague Dawley Inc., Indianapolis Ind.) were subcutaneously immunized once per week for 3 weeks with sterile phosphate-buffered saline (PBS) as a control. All of the animals immunized with FLL32 and five of the ten animals immunized with PBS were then challenged 2 weeks after the final immunization by subcutaneous injection of a P. gingivalis W83 wild-type suspension containing 1×10¹⁰ cells, a dosage of 5×10⁵ bacteria per kg of body weight. The remaining five animals immunized with PBS were challenged 2 weeks after the final immunization by subcutaneous injection of PBS as a control.

By 24 hours post-challenge, one of the five control animals immunized with PBS and challenged with P. gingivalis W83 died and the other four animals had developed spreading infections with secondary site abdominal skin ulcerations and, in some, primary site ulcerations around the base of the tail. All of these mice exhibited severe cachexia with ruffled hair, hunched bodies and weight loss; and all of these five control animals died by four days post-challenge.

In contrast, eight of sixteen animals immunized with P. gingivalis FLL32 and challenged with P. gingivalis W83 displayed only minor secondary skin site abdominal infections by 24 hours post-challenge but all recovered and were alive at the end of the test period. Of the remaining eight animals immunized with P. gingivalis FLL32 and challenged with P. gingivalis W83, five had severe cachexia and died by three days post-challenge, two had moderate cachexia and developed secondary ulcerating abdominal lesions which began to heal at day 5 post-challenge and were alive at the end of the fourteen day experiment period, and the last animal developed a secondary lesion which healed but then developed an additional secondary lesion and died at day 7 post-challenge.

All of the five animals immunized with PBS and challenged with PBS appeared normal throughout the fourteen day experiment period.

The results of these challenges were analyzed using Fisher's Exact Test. The analysis found that immunization with the FLL32 strain protected the animals from a wild-type challenge (p=0.148), while those animals that were immunized with sterile phosphate-buffered saline were not protected (p=0.023).

At the end of the fourteen day experiment period, the ten surviving animals from the group originally immunized with FLL32 and then challenged with W83, and the five animals immunized with PBS and challenged with PBS were sacrificed and their sera were isolated to ascertain the presence of anti-FLL32 antibodies. A 1:1000 dilution of the sera was tested by Western blot analysis for cross-reactivity to whole cell lysates of P. gingivalis W83, FLL32 and FLL33.

Animals immunized with FLL32 were positive for antibodies to each of the P. gingivalis whole cell lysates (data not shown). Immunoreactive bands with molecular mass of 96, 82, 74, 55.2, 49.6, 38, 37, and 35 kDa were observed in the Western blot analyses of each of the whole cell lysates of FLL32, FLL33 and W83. Immunoreactive bands with molecular mass of 44 and 40 kDa were present in the Western blot analyses of each of the whole cell lysates of FLL33 and W83 but were absent from the Western blot analysis of the whole cell lysates of FLL32. Further, immunoreactive bands with molecular mass of 185, 170, 125, 71, 68, 63 and 47 kDa were present in the Western blot analyses of whole cell lysates of FLL32 but were absent in the Western blot analysis of each of the whole cell lysates of FLL33 and the W83 strain.

In contrast, sera from animals immunized with PBS and challenged with PBS were negative for antibodies to each of the P. gingivalis whole cell lysates.

EXAMPLE III Method of Decreasing the Growth Rate or Reproduction Rate of Porphyromonas gingivalis in a Mammal

According to one embodiment of the present invention, there is provided a method of decreasing the growth rate or reproduction rate of Porphyromonas gingivalis in a mammal, such as a human. The method comprises the step of administering to the mammal at least one dose of a non-virulent, recA⁻ mutant of Porphyromonas gingivalis, such as FLL32. The dose can be administered, for example, by subcutaneous, intramuscular or intravenous injection. In a preferred embodiment, the dosage is between about 1×10³ and 1×10⁷ bacteria per kg of body weight. In a particularly preferred embodiment, the dosage is between about 1×10⁵ and 1×10⁶ bacteria per kg of body weight.

Among the uses of decreasing the growth rate or reproduction rate of Porphyromonas gingivalis in a mammal, such as a human, is the prevention or treatment of periodontitis, or other diseases or conditions caused in whole or in part by Porphyromonas gingivalis, such as aspiration pneumonia and necrotizing pneumonia, abscesses in brain, genitourinary tract and lung, and mediastinitis.

Although the present invention has been discussed in considerable detail with reference to certain preferred embodiments, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of preferred embodiments contained herein. 

I claim:
 1. The Porphyromonas gingivalis strain which is deposited at ATCC under accession number
 202109. 2. A pharmaceutical preparation comprising the mutant of Porphyromonas gingivalis according to claim
 1. 